Along with the slowing of the speed in which the processing performances of the individual computers are enhanced, or with the reduction of costs of the computer devices, there have been proposed various types of distribution processing methods for realizing processing of enormous amounts of data with improved performance by arranging a large number of computers. In order to efficiently perform distribution processing, it is important to enhance the expandability of the number of computers by reducing the amount of communication among computers during processing. Patent literature 1 discloses a “MapReduce” technique in which the target data to be processed is divided among computers and assigned to respective computers, wherein the processing of data assigned to each respective computer is performed by each computer, and the result of processing is assembled at the end. According to “MapReduce”, during data processing, each computer refers to the data assigned to it, so that there is no need to communicate with other computers, but the expandability of the number of computers can be maintained.
According to the “MapReduce” technique, the expandability of the number of computers is maintained by not having to refer to the data in other computers, but on the other hand, once the data is assigned to a computer, if the number of computers is increased or decreased after assignment, data must be moved among computers, according to which the time required for increasing and decreasing the number of computers is elongated if the amount of data is enormous.
One possible method for preventing data movement when the number of computers is increased or decreased is to share the data among computers. One example of such method is a cluster file system constructing a shared file system by sharing disks among computers and only communicating the storage location information of data via nodes. Patent literature 2 illustrates an example of a cluster file system. However, generally according to the cluster file system, the management of the storage location information of data is either concentrated to one portion of the computers or distributed among all computers, but if the number of computers is increased, performance bottleneck occurs, by which the expandability of the number of computers is restricted.